Methods for Manufacturing Multi-Layer Rotationally Molded Parts

ABSTRACT

This invention relates generally to methods of rotationally molding multi-layer parts. More particularly, in certain embodiments, the invention relates to methods of manufacturing a part having an interior layer of polymerized macrocyclic polyester oligomer and an exterior layer of a substantially non-oligomeric polymer. The invention also relates to methods of manufacturing a part with a scratch resistant surface.

PRIOR APPLICATION

This application claims priority to and benefit under 35 U.S.C. 119(e)of U.S. Provisional Patent Application No. 60/856,459, filed Nov. 3,2006, the text of which is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

This invention relates generally to methods of rotationally moldingmultiple-layer parts. More particularly, in certain embodiments, theinvention relates to the rotational molding of a multi-layer part usinga single charge containing macrocyclic polyester oligomer andnon-oligomeric polymer.

BACKGROUND OF THE INVENTION

Multiple-layer manufactured parts are useful, for example, where it isdesired that properties of the interior and exterior of the part differ,or where it is only necessary that one layer be made from a specialmaterial, while the remainder of the part can be made of less expensivematerial.

For example, double layer gasoline tanks (or other fuel tanks) may bemanufactured with an interior layer having very low gasoline (or otherfuel) permeability and with an exterior layer that has high impactresistance. Such parts may be rotationally molded.

The manufacture of multiple-layer parts typically requires multiplecharges. For example, a rotational mold is charged with polymergranules, which are melted and rotated, then cooled, thereby forming theouter layer of a two-layer part. Then, a different polymer is fed intothe mold, rotated, and cooled to form the inner layer. The inner polymermay have a lower melting point than the outer polymer, and the interiortemperature of the mold in the second step may be held between themelting points of the two polymers so that the outer layer stays solidwhile the inner layer is being rotationally molded.

Drop boxes have been used to simplify the rotational molding ofmulti-layer parts with multiple charges. The drop box usually mounts onthe outside of the mold and holds a second charge of material. After thefirst charge inside the mold cavity has formed the exterior layer of themolded part, an air actuated cylinder inside the drop box releases thesecond charge into the mold to form the interior layer. Drop box methodsare still more complex than single charge processes, and generallyrequire more processing time.

Single charge processing is possible where the outer layer polymer has alower melting temperature than the inner layer polymer. It is possibleto charge the rotational mold with particles of both polymers, then heatand rotate the mold to form the part from the single charge. Theparticles of the outer layer polymer melt first and stick to the wall ofthe mold while the particles of the inner layer polymer remain solid.Then, the inner layer polymer melts and rotation continues until an eveninterior coating is achieved.

However, in practice, particles of the inner layer polymer can becometrapped in the outer layer, and a greater amount of inner layer polymeris needed to form an even interior coating. This is particularlyproblematic where the inner layer polymer is an expensive material.Furthermore, the properties of the part, including its appearance, maybe adversely affected by the presence of interior layer polymer trappedin the outer layer. For example, there may be gaps or ruptures withinthe part or at the exterior or interior surfaces of the part due to thetrapped material.

Single-charge rotational molding processes are less expensive to runthan multiple-charge processes because they require less time and areless complex. However, the problem of entrapment of inner layer polymerin the outer layer may require using more of the expensive inner layerpolymer. The entrapped polymer may also have deleterious effects on theappearance and/or function of the manufactured part.

Thus, there is a need for efficient methods of manufacturing multi-layerparts with reduced entrapment of polymer particles between the layers.

SUMMARY OF THE INVENTION

A double-layered fuel tank or other multi-layer part can be rotationallymolded with a tough, durable exterior and with an interior having verylow gasoline (or other fluid) permeability, where the interior layer ismade from a macrocyclic polyester oligomer (MPO), and the exterior layeris made from a non-oligomeric polymer such as polyethylene. Thepolymerized MPO layer provides extremely low gasoline permeability onthe interior of the part, while the molded polyethylene (optionallycross-linked) provides an inexpensive, durable exterior.

In a preferred embodiment, a rotational mold is initially charged withboth an MPO and a non-oligomeric polymer. The invention substantiallyreduces or eliminates entrapment of polymer particles in rotationallymolded multi-layer parts, without requiring that the mold be separatelycharged with material to build each layer. The problem of entrappedparticles is solved by: (i) initially charging the mold with theinterior layer material contained inside a plastic bag; and/or (ii)initially charging the mold with the interior layer material in the formof particles that are sufficiently large and/or heavy to prevent themfrom sticking in the melting exterior layer material.

For example, in one embodiment, a rotational mold is initially chargedwith solid polyethylene particles as well as solid MPO particles,wherein the MPO particles are contained within a plastic bag and/or theMPO particles are sufficiently large that they do not stick in themelting polyethylene during mold rotation.

Where a plastic bag is used, release of the MPO is delayed during therotational molding cycle, allowing the substantially non-oligomericpolymer (e.g., polyethylene) to partially or completely melt, coat theinterior of the mold, and/or cross-link. The delayed release prevents orreduces embedding of the MPO in the exterior polyethylene layer. Theplastic bag becomes incorporated in the part without detrimentaleffects.

The plastic bag may be any plastic container of any configuration. Oneor more plastic bags may be used, and/or the characteristics of the bagmay be tailored to a given process to provide an adequately delayedrelease of melted/melting MPO (e.g. bag thickness, material, weave,etc., can be varied). Parts with two or more layers may be manufactured,for example, by charging the mold with different bags containingdifferent layer materials, the bags having different melt or rupturecharacteristics such that their contents are released at different timesduring the rotational molding cycle, thereby allowing greater control ofthe distribution of materials within different layers. For example, themore interior layers may be initially contained in bags that melt orrupture later in the cycle.

The plastic bag(s) may contain fillers, including catalysts,cross-linking agents, and/or reinforcing agents to be used in one ormore separate layers. For example, a rotational mold can be initiallycharged with a stone-filled cyclic poly(butylene terephthalate) oligomer(cPBT) with polymerization catalyst to form the outer layer of the part,and at the same time, the rotational mold is also charged with a plasticbag containing glass fiber reinforcement and oligomer or polymer to formthe inner layer. The outer stone-filled layer provides good aesthetics,while the glass-filled layer provides strength.

Using MPO particles having an average thickness greater than thethickness of the outer layer of the multi-layer part reduces oreliminates the problem of embedded MPO in the outer layer. For example,in an embodiment where the particles are roughly spherical, the MPOparticles used may have average radius greater than the thickness of theouter layer. For example, where the outer layer is made withpolyethylene and the inner layer is made with cyclic poly(butyleneterephthalate) oligomer (cPBT), the size and weight of the cPBTparticles pulls them out of the melted/melting polyethylene layer as themold rotates, avoiding or preventing entrapment.

These large particles are optionally contained within a plastic bag uponinitial charging of the mold, to delay release of the MPO and molding ofthe MPO layer. In certain embodiments, the large particles are notcontained within a plastic bag, but are simply introduced into the moldalong with the exterior layer material before rotational molding begins.The MPO particles are preferably large and/or heavy enough to “pull out”of the melting exterior layer material as the mold rotates early in thecycle. Then, as the MPO particles melt, the MPO polymerizes in the moldto form the interior layer of the part.

The rotational molding methods described herein are not limited to useof MPO. For example, the methods may be used to manufacture multi-layerparts with polyethylene in one layer and one or more other plastics,such as nylon, in another layer.

The plastic bag may also be used to control the release of MPO in makingthick walled parts, for example, parts over about ⅛″ [3 mm] thick.Rotational molding of a large amount of MPO resin, for example, cyclicpoly(butylene terephthalate) oligomer, at one time may lead to unevenwall thickness distribution in rotationally molded parts. One or moreplastic bags may be used to control the release of MPO at differenttimes and temperatures. By effectively dividing one charge into severalsmall charges in the mold, the wall thickness distribution is improved.Thus, both release and coverage of an inner resin layer of therotationally molded part can be controlled using sacrificial plasticcontainers in a single charge.

Where the exterior layer material is polyethylene (PE) and the MPO iscyclic poly(butylene terephthalate) oligomer (cPBT), the PE melts atabout 120° C. while the cPBT starts melting at about 160° C. When the PEbegins to melt, it adheres to the wall of the mold, while the cPBT isstill solid and is rolling in the mold. The use of a bag to initiallycontain the cPBT helps prevent the cPBT particles becoming trapped inthe PE layer. Alternatively, or additionally, the use of large and/orheavy cPBT particles helps the cPBT “pull out” of the melting PE layeras the mold rotates, for at least part of the time during which the PElayer is being formed.

In addition to providing low fluid permeability, a layer made withpolymerized MPO offers excellent scratch resistance. Thus, in oneembodiment, the invention provides a method of rotationally molding amulti-layer part using a single initial charge of (i) an MPO for formingthe exterior layer with scratch resistant surface and (ii) asubstantially non-oligomeric polymer for forming an interior layer.Various embodiments make use of a plastic bag containing thenon-oligomeric polymer for delayed release and/or better controlledcoverage, allowing the MPO to coat the mold before release ofnon-oligomeric polymer.

Additionally or alternatively, melted MPO can be used to coat particlesof the interior layer non-oligomeric polymer (e.g., polyethyleneparticles). The melted MPO may or may not contain catalyst, and even ifit contains catalyst, the MPO should not polymerize significantly duringthe coating process, as coating requires low residence time andrelatively low temperature. The coated polyethylene particles may thenbe placed in a rotational mold in a single charge with the MPO. The MPOpolymerizes to form a scratch-resistant outer layer with thepolyethylene dispersed therein, thereby improving impact strength.

In one aspect, the invention relates to a method of manufacturing amulti-layer part, the method including the steps of: (a) charging arotational mold with at least a substantially non-oligomeric polymer anda macrocyclic polyester oligomer, wherein the macrocyclic polyesteroligomer is initially contained within one or more plastic bags; and (b)rotating the mold, the mold having an elevated interior temperature.

The substantially non-oligomeric polymer may include one or more of thefollowing: polyethylene, polybutylene, polypropylene, polystyrene,polyethylene terephthalate, polybutylene terephthalate, polyamide,polyester, polyvinyl chloride, polycarbonate, acrylonitrile butadienestyrene, nylon, polyurethane, polyacetal, and/or polyvinylidenechloride, for example. The substantially non-oligomeric polymer mayinclude a crosslinked polymer, for example, crosslinked polyethylene,and/or a thermoplastic polyolefin.

The macrocyclic polyester oligomer may include a macrocyclicpoly(alkylene dicarboxylate) oligomer having a structural repeat unit ofthe formula:

where A is an alkylene, or a cycloalkylene or a mono- or polyoxyalkylenegroup; and B is a divalent aromatic or alicyclic group. For example, themacrocyclic polyester oligomer may include one or more of the following:macrocyclic poly(butylene terephthalate) oligomer, macrocyclicpoly(propylene terephthalate) oligomer, macrocyclicpoly(cyclohexylenedimethylene terephthalate) oligomer, macrocyclicpoly(ethylene terephthalate) oligomer, macrocyclic poly(1,2-ethylene2,6-naphthalenedicarboxylate) oligomer, and copolyester oligomercomprising two or more monomer repeat units.

In a preferred embodiment, the melting temperature of the macrocyclicpolyester oligomer is higher than the melting temperature of thenon-oligomeric polymer. In certain embodiments, the substantiallynon-oligomeric polymer includes polyethylene, and the macrocyclicpolyester oligomer comprises macrocyclic poly(butylene terephthalate)oligomer.

In certain embodiments, the mold is also initially charged with afiller. The filler may include, for example, one or more of thefollowing: a polymerization catalyst, a cross-linking agent, glass,glass fiber, milled glass fiber, glass microspheres, micro-balloons,stone, crushed stone, nanoclay, graphite, carbon nanotubes, carbonblack, carbon fibers, buckminsterfullerene, anhydrous talc, fumedsilica, titanium dioxide, calcium carbonate, wollastonite, choppedfiber, fly ash, linear polymer, monomer, branched polymer, engineeringresin, impact modifier, organoclay, and/or pigment.

The plastic bag may be made of one or more of the following:polyethylene, high density polyethylene (HDPE), low density polyethylene(LDPE), polylactide, and/or starch (e.g., for biodegradable bags). Incertain embodiments, during step (b), the macrocyclic polyester oligomer(MPO) begins to melt before the plastic bag. Furthermore, in certainembodiments, the substantially non-oligomeric polymer begins to meltbefore the MPO and before the plastic bag.

The interior air temperature of the mold may reach at least about 200°C. during step (b), wherein the substantially non-oligomeric polymerbegins to melt at about 120° C., and wherein the macrocyclic polyesteroligomer begins to melt at a temperature above about 120° C. In certainembodiments, the interior air temperature of the mold reaches at leastabout 220° C., about 230° C., about 240° C., or about 250° C. In certainembodiments, the difference in the melting temperature of the MPO andthe substantially non-oligomeric polymer is at least about 20° C., atleast about 25° C., at least about 30° C., at least about 35° C., or atleast about 40° C.

In a preferred embodiment, step (a) includes charging the rotationalmold with the MPO and the substantially non-oligomeric polymer in onestep. In alternative embodiments, the rotational mold may be charged intwo or more separate steps, and/or may be continuously orsemi-continuously charged during the molding process. The description ofelements of the embodiments elsewhere herein can be applied in thisaspect of the invention as well.

In another aspect, the invention relates to a method of manufacturing amulti-layer part, the method including the steps of: (a) charging arotational mold with at least the following: a substantiallynon-oligomeric polymer for forming an exterior layer of the multi-layerpart; and particles including MPO for forming an interior layer of themulti-layer part, wherein the particles including the MPO average atleast about ⅛″ in at least one dimension; and (b) rotating the mold, themold having an elevated interior temperature. The description ofelements of the embodiments above and elsewhere herein can be applied inthis aspect of the invention as well.

In certain embodiments, the particles including the MPO average at leastabout ¼″, at least about ½″, at least about ¾″, at least about 1″, atleast about 1¼″, or at least about 1½″ in at least one dimension. The atleast one dimension may include, for example, thickness and/or length(e.g. for pellets or pastilles), and/or diameter and/or radius (e.g.,for spherical or roughly spherical particles). In certain embodiments,at least half of the particles including the MPO are larger in at leastone dimension than the thickness of the exterior layer of themulti-layer part. The particles may be substantially spherical,substantially cylindrical, and/or the particles may have an irregularshape. In certain embodiments, the particles have an average radiusgreater than the thickness of the exterior layer of the multi-layerpart. In certain embodiments, the particles are sized such that theynumber about 60 or fewer particles per gram, about 50 or fewer particlesper gram, about 40 or fewer particles per gram, about 35 or fewerparticles per gram, about 30 or fewer particles per gram, about 25 orfewer particles per gram, about 20 or fewer particles per gram, about 15or fewer particles per gram, about 10 or fewer particles per gram, about5 or fewer particles per gram, about 4 or fewer particles per gram,about 3 or fewer particles per gram, about 2 or fewer particles pergram, or about 1 particle per gram.

In certain embodiments, the particles including MPO are contained withinone or more plastic bags. For example, in certain embodiments, thesubstantially non-oligomeric polymer begins to melt before the MPO andbefore the plastic bag.

In another aspect, the invention relates to a method of manufacturing amulti-layer part, the method including the steps of: (a) charging arotational mold with at least: (i) a substantially non-oligomericpolymer for forming an exterior layer of the multi-layer part, and (ii)MPO particles for forming an interior layer of the multi-layer part,where the MPO particles have an average thickness greater than thethickness of the exterior layer of the multi-layer part; and (b)rotating the mold, the mold having an elevated interior temperature. Thedescription of elements of the embodiments above and elsewhere hereincan be applied in this aspect of the invention as well. In certainembodiments, the MPO particles have an average radius greater than thethickness of the exterior layer of the multi-layer part. In certainembodiments, the substantially non-oligomeric polymer includes one ormore of the following: polyethylene, crosslinked polyethylene,polybutylene, polypropylene, polystyrene, polyethylene terephthalate,polybutylene terephthalate, polyamide, polyester, polyvinyl chloride,polycarbonate, acrylonitrile butadiene styrene, nylon, polyurethane,polyacetal, and polyvinylidene chloride.

In yet another aspect, the invention relates to a method ofmanufacturing a part with a scratch-resistant outer surface, the methodincluding the steps of: (a) charging a rotational mold with at least asubstantially non-oligomeric polymer and an MPO for forming thescratch-resistant surface of the part, wherein the substantiallynon-oligomeric polymer is initially contained within a plastic bag; and(b) rotating the mold, the mold having an elevated interior temperature,wherein the MPO begins to melt before the plastic bag. The descriptionof elements of the embodiments above and elsewhere herein can be appliedin this aspect of the invention as well.

In still another aspect, the invention relates to a method ofmanufacturing a part with a scratch-resistant surface, the methodincluding the steps of: (a) coating particles including a substantiallynon-oligomeric polymer with an at least partially molten MPO; (b)charging a rotational mold with at least the coated particles from step(a); and (c) rotating the mold, the mold having an elevated interiortemperature. The description of elements of the embodiments above andelsewhere herein can be applied in this aspect of the invention as well.For example, certain portions of the charge may be bagged and/or largeparticles may be used to reduce or eliminate intermingling of componentsof the various layers of the multi-layer part.

In another aspect, the invention relates to a method of manufacturing apart with a scratch-resistant surface, the method comprising the stepsof contacting a surface of a rotational mold with melted MPO, thenintroducing a substantially non-oligomeric polymer into the mold. Thedescription of elements of the embodiments above and elsewhere hereincan be applied in this aspect of the invention as well. The step ofcontacting a surface of the rotational mold with melted MPO may includeintroducing solid particles made at least partially of MPO into the moldand melting the solid particles in the mold. In another embodiment, thestep of contacting the surface of the rotational mold with melted MPOincludes introducing melted MPO into the mold. In certain embodiments,the step of introducing a substantially-non-oliogmeric polymer into themold is performed using a drop box. The drop box may be located outsidethe mold or inside the mold, for example. In certain embodiments, thedrop box mounts on the outside of the mold and holds the substantiallynon-oligomeric polymer. For example, after the first charge inside themold cavity (including or consisting of MPO) has coated the interiorsurface of the mold, an air actuated cylinder inside the drop boxreleases the second charge into the mold.

BRIEF DESCRIPTION OF THE DRAWING

The objects and features of the invention can be better understood withreference to the drawings described below, and the claims. The drawingsare not necessarily to scale, emphasis instead generally being placedupon illustrating the principles of the invention. In the drawings, likenumerals are used to indicate like parts throughout the various views.

FIG. 1 depicts pellets of cyclic poly(butylene terephthalate) oligomerused in a rotational molding process, according to an illustrativeembodiment of the invention.

FIG. 2 depicts pellets of cyclic poly(butylene terephthalate) oligomersealed in 4 mil polyethylene bags, where a rotational mold is initiallycharged with the bags, according to an illustrative embodiment of theinvention.

FIG. 3 depicts a rotational mold initially charged with polyethylenepowder and bagged cyclic poly(butylene terephthalate) oligomer,according to an illustrative embodiment of the invention.

FIG. 4 depicts a two-layer rotationally molded part made with the moldinitially charged with bagged MPO, and a part made with the moldinitially charged with unbagged MPO, according to illustrativeembodiments of the invention.

DETAILED DESCRIPTION

Throughout the description, where reagents, reactants, and products aredescribed as having, including, or comprising one or more specificcomponents, or where processes and methods are described as having,including, or comprising one or more specific steps, it is contemplatedthat, additionally, there are reagents, reactants, and products of thepresent invention that consist essentially of, or consist of, the one ormore recited components, and that there are processes and methodsaccording to the present invention that consist essentially of, orconsist of, the one or more recited processing steps.

It should be understood that the order of steps or order for performingcertain actions is immaterial, as long as the invention remainsoperable. Moreover, two or more steps or actions may be conductedsimultaneously.

Scale-up and/or scale-down of systems, processes, units, and/or methodsdisclosed herein may be performed by those of skill in the relevant art.Processes described herein are generally configured for batch operation,but also include continuous or semi-continuous processes.

The headers are provided herein as a general organizational guide and donot serve to limit support for any given element of the invention to aparticular section of the specification.

DEFINITIONS

As used herein, “macrocyclic” is understood to mean a cyclic moleculehaving at least one ring within its molecular structure that contains 5or more atoms covalently connected to form the ring.

As used herein, an “oligomer” is understood to mean a molecule thatcontains from two to seven identifiable structural repeat units of thesame or different formula.

As used herein, a “non-oligomeric polymer” is understood to mean apolymer that contains at least 8 structural repeat units of the same ordifferent formula. The physical properties of an oligomer generally varywith the addition or removal of one of the structural repeat units,while the physical properties of a non-oligomeric polymer generally donot appreciably vary with the addition or removal of one of thestructural repeat units.

As used herein, a “macrocyclic polyester oligomer” (MPO) is understoodto mean a macrocyclic oligomer containing structural repeat units havingan ester functionality. A macrocyclic polyester oligomer typicallyrefers to multiple molecules of one specific repeat unit formula.However, a macrocyclic polyester oligomer also may include multiplemolecules of different or mixed formulae having varying numbers of thesame or different structural repeat units. In addition, a macrocyclicpolyester oligomer may be a co-polyester or multi-component polyesteroligomer, i.e., an oligomer having two or more different structuralrepeat units having ester functionality within one cyclic molecule.

As used herein, “substantially homo- or co-polyester oligomer” isunderstood to mean a polyester oligomer wherein the structural repeatunits are substantially identical or substantially composed of two ormore different structural repeat units, respectively.

As used herein, an “alkylene group” is understood to mean —C_(a)H_(2n)—,where n≧2.

As used herein, a “cycloalkylene group” is understood to mean a cyclicalkylene group, —C_(n)H_(2n-x)—, where x represents the number of H'sreplaced by cyclization(s).

As used herein, a “mono- or polyoxyalkylene group” is understood to mean[—(CH₂)_(m)—O—]_(n)—(CH₂)_(m)—, wherein m is an integer greater than 1and n is an integer greater than 0.

As used herein, a “divalent aromatic group” is understood to mean anaromatic group with links to other parts of the macrocyclic molecule.For example, a divalent aromatic group may include a meta- orpara-linked monocyclic aromatic group (e.g., benzene).

As used herein, an “alicyclic group” is understood to mean anon-aromatic hydrocarbon group containing a cyclic structure within.

As used herein, a “C₁₋₄ primary alkyl group” is understood to mean analkyl group having 1 to 4 carbon atoms connected via a primary carbonatom.

As used herein, a “C₁₋₁₀ alkyl group” is understood to mean an alkylgroup having 1 to 10 carbon atoms, including straight chain or branchedradicals.

As used herein, a “methylene group” is understood to mean —CH₂—.

As used herein, an “ethylene group” is understood to mean —CH₂—CH₂—.

As used herein, a “C₂₋₃ alkylene group” is understood to mean—C_(n)H_(2n)—, where n is 2 or 3.

As used herein, a “C₂₋₆ alkylene group” is understood to mean—C_(n)H_(2n)—, where n is 2-6.

As used herein, “substitute phenyl group” is understood to mean a phenylgroup having one or more substituents. A substituted phenyl group mayhave substitution pattern that is recognized in the art. For example, asingle substituent may be in the ortho, meta or para positions. Formultiple substituents, typical substitution patterns include, forexample, 2,6-, 2,4,6-, and, 3,5-substitution patterns.

As used herein, a “filler” is understood to mean a material added to amacrocyclic polyester oligomer and/or non-oligomeric polymer inmanufacturing a part. A filler may be used to achieve a desired purposeor property (e.g., physical, mechanical, chemical, electrical, and/orthermal property(ies)), and may be present or transformed into knownand/or unknown substances in the resulting part. For example, thepurpose of the filler may be to provide stability, such as chemical,thermal, or light stability; to increase the strength of the part (orlayer thereof); and/or to increase electrical and/or thermalconductivity of the part (or layer thereof). A filler also may provideor reduce color, provide weight or bulk to achieve a particular density,provide reduced gas, liquid, and/or vapor permeability, provide flame orsmoking resistance (i.e., be a flame retardant), be a substitute for amore expensive material, facilitate processing, and/or provide otherdesirable properties. Illustrative examples of fillers are, amongothers, polymerization catalysts, cross-linking agents, graphite, carbonnanotubes, carbon black, carbon fibers, anhydrous magnesium silicate(anhydrous talc), fumed silica, titanium dioxide, calcium carbonate,aluminum (e.g., aluminum powder), wollastonite, chopped fibers, fly ash,glass, glass fiber, milled glass fiber, microspheres (e.g., glass orpolymeric; hollow, partially hollow, or filled), nanospheres (e.g.,glass or polymeric; hollow, partially hollow, or filled),micro-balloons, crushed stone, nanoclay, linear polymers, monomers,branched polymers, engineering resin, impact modifiers, organoclays, andpigments. Multiple fillers may be included, for example, to achieve abalance of properties.

Macrocyclic Polyester Oligomers

Many different MPOs can readily be made and are useful in the practiceof this invention. MPOs that may be employed in this invention include,but are not limited to, macrocyclic poly(alkylene dicarboxylate)oligomers having a structural repeat unit of the formula:

where A is an alkylene, or a cycloalkylene or a mono- or polyoxyalkylenegroup; and B is a divalent aromatic or alicyclic group.

Preferred MPOs include macrocyclic poly(1,4-butylene terephthalate)(cPBT), macrocyclic poly(1,3-propylene terephthalate) (cPPT),macrocyclic poly(1,4-cyclohexylenedimethylene terephthalate) (cPCT),macrocyclic poly(ethylene terephthalate) (PET), and macrocyclicpoly(1,2-ethylene 2,6-naphthalenedicarboxylate) (cPEN) oligomers, andcopolyester oligomers comprising two or more of the above monomer repeatunits.

MPOs may be prepared by known methods. Synthesis of the preferred MPOsmay include the step of contacting at least one diol of the formulaHO-A-OH with at least one diacid chloride of the formula:

where A and B are as defined above. The reaction typically is conductedin the presence of at least one amine that has substantially no sterichindrance around the basic nitrogen atom. An illustrative example ofsuch amines is 1,4-diazabicyclo[2.2.2]octane (DABCO). The reactionusually is conducted under substantially anhydrous conditions in asubstantially water immiscible organic solvent such as methylenechloride. The temperature of the reaction typically is between about−25° C. and about 25° C. See, e.g., U.S. Pat. No. 5,039,783 to Brunelleet al.

MPOs have also been prepared via the condensation of a diacid chloridewith at least one bis(hydroxyalkyl) ester such as bis(4-hydroxybutyl)terephthalate in the presence of a highly unhindered amine or a mixturethereof with at least one other tertiary amine such as triethylamine, ina substantially inert organic solvent such as methylene chloride,chlorobenzene, or a mixture thereof. See, e.g., U.S. Pat. No. 5,231,161to Brunelle et al.

Another method for preparing MPOs is to depolymerize linear polyesterpolymers in the presence of an organotin or titanate compound. In thismethod, linear polyesters are converted to macrocyclic polyesteroligomers by heating a mixture of linear polyesters, an organic solvent,and a trans-esterification catalyst such as a tin or titanium compound.The solvents used, such as o-xylene and o-dichlorobenzene, usually aresubstantially free of oxygen and water. See, e.g., U.S. Pat. Nos.5,407,984 to Brunelle et al. and 5,668,186 to Brunelle et al.

MPOs have been prepared from intermediate molecular weight polyesters bycontacting a dicarboxylic acid or a dicarboxylate in the presence of acatalyst to produce a composition comprising a hydroxyalkyl-terminatedpolyester oligomer. The hydroxyalkyl-terminated polyester oligomer isheated to produce a composition comprising an intermediate molecularweight polyester which preferably has a molecular weight between about20,000 Daltons and about 70,000 Daltons. The intermediate molecularweight polyester is heated and a solvent is added prior to or during theheating process to produce a composition comprising an MPO. See, e.g.,U.S. Pat. No. 6,525,164, to Faler.

MPOs that are substantially free from macrocyclic co-oligoesters havebeen prepared by depolymerizing polyesters using the organo-titanatecatalysts described in U.S. Pat. No. 6,787,632, by Phelps et al. It isalso within the scope of the invention to employ macrocyclic homo- andco-polyester oligomers to produce homo- and co-polyester polymers,respectively. Therefore, unless otherwise stated, an embodiment of acomposition, article, process, or method that refers to a macrocyclicpolyester oligomer also includes a co-polyester embodiments.

In one embodiment, macrocyclic ester homo- and co-oligomers used in thisinvention include oligomers having a general structural repeat unit ofthe formula:

where A′ is an alkylene, cycloalkylene, or mono- or polyoxyalkylenegroup, and where A′ may be substituted, unsubstituted, branched, and/orlinear. Example MPOs of this type include butyrolactone andcaprolactone, where the degree of polymerization is one, and2,5-dioxo-1,4-dioxane, and lactide, where degree of polymerization istwo. The degree of polymerization may alternatively be 3, 4, 5, orhigher.

In one embodiment, a macrocyclic polyester oligomer (MPO) includesspecies of different degrees of polymerization. Here, a degree ofpolymerization (DP) with respect to the MPO means the number ofidentifiable structural repeat units in the oligomeric backbone. Thestructural repeat units may have the same or different molecularstructure. For example, an MPO may include dimer, trimer, tetramer,pentamer, and/or other species.

MPO Polymerization Catalyst

Polymerization catalysts employed in certain embodiments of theinvention are capable of catalyzing the polymerization of MPO. As withstate-of-the-art processes for polymerizing MPOs, organotin andorganotitanate compounds are the preferred catalysts, although othercatalysts may be used. For example, butyltin chloride dihydroxide (i.e.n-butyltin(IV) chloride dihydroxide) may be used as polymerizationcatalyst. Other illustrative organotin compounds include dialkyltin(IV)oxides, such as di-n-butyltin(IV) oxide and di-n-octyltin oxide, andacyclic and cyclic monoalkyltin (IV) derivatives such as n-butyltintri-n-butoxide, dialkyltin(IV) dialkoxides such as di-n-butyltin(IV)di-n-butoxide and 2,2-di-n-butyl-2-stanna-1,3-dioxacycloheptane, andtrialkyltin alkoxides such as tributyltin ethoxide. Another illustrativeorganotin compound that may be used as polymerization catalyst is1,1,6,6-tetra-n-butyl-1,6-distanna-2,5,7,10-tetraoxacyclodecane. See,e.g., U.S. Pat. No. 5,348,985 to Pearce et al.

Also, trisstannoxanes having the general formula (I) shown below can beused as a polymerization catalyst to produce branched polyesterpolymers.

where R₂ is a C₁₋₄ primary alkyl group and R₃ is C₁₋₁₀ alkyl group.

Additionally, organotin compounds with the general formula (II) shownbelow can be used as a polymerization catalyst to prepare branchedpolyester polymers from macrocyclic polyester oligomers.

where R₃ is defined as above.

As for titanate compounds, tetra(2-ethylhexyl) titanate, tetraisopropyltitanate, tetrabutyl titanate, and titanate compounds with the generalformula (III) shown below can be used as polymerization catalysts.

wherein: each R₄ is independently an alkyl group, or the two R₄ groupstaken together form a divalent aliphatic hydrocarbon group; R₅ is aC₂₋₁₀ divalent or trivalent aliphatic hydrocarbon group; R₆ is amethylene or ethylene group; and n is 0 or 1.

Typical examples of titanate compounds with the above general formulaare shown in Table 1.

TABLE 1 Examples of Titanate Compounds Having Formula (III)

Titanate ester compounds having at least one moiety of the followinggeneral formula have also been used as polymerization catalysts:

wherein: each R₇ is independently a C₂₋₃ alkylene group; R₈ is a C₁₋₆alkyl group or unsubstituted or substituted phenyl group; Z is O or N;provided when Z is O, m=n=0, and when Z is N, m=0 or 1 and m+n=1; eachR₉ is independently a C₂₋₆ alkylene group; and q is 0 or 1.

Typical examples of such titanate compounds are shown below as formula(VI) and formula (VII):

Other polymerization catalysts which may be used include aryl titanates,described, for example, in U.S. Pat. No. 6,906,147, by Wang. Also,polymer-containing organo-metal catalysts may be used in the invention.These include the polymer-containing catalysts described in U.S. Pat.No. 6,831,138, by Wang.

EXPERIMENTAL EXAMPLES

The experimental examples demonstrate manufacture of multi-layer partsvia single-charge rotational molding. The parts include an interiorlayer containing polymerized MPO and an exterior layer containingpolyethylene.

The experiments use solid pellets of macrocyclic polyester oligomermanufactured by Cyclics Corporation of Schenectady, N.Y., that areprimarily composed of macrocyclic poly(1,4-butylene terephthalate)oligomer. The MPO used in the experiments is sold as CBT160® and isreferred to hereinbelow as cPBT, for simplicity. The pellets alsocontain 0.5 wt. % Fascat® 4105 organotin polymerization catalyst,manufactured by Arkema, Inc., of Philadelphia, Pa. The pellets areapproximately ¼″ long and approximately ⅛″ in diameter.

The experiments also use solid polyethylene (PE) powder manufactured byExxonMobil Chemical of Ontario, Canada, sold as ExxonMobil HDP8660. Thepowder has 95% of the particles smaller than about 500 micron (about 35mesh).

Two-Layer Rotationally Molded Part: PE and Unbagged cPBT Vs. PE andBagged cPBT

A double-layer box with approximate dimensions 14″×10″×3.5″ wasrotomolded with a single charge containing PE and cPBT. Experiments wereconducted both with and without the use of a bag to initially containthe cPBT resin, then compared visually.

The cPBT pellets were dried in an 80° C. desiccant dryer for at least 20hours. The rotational mold was charged with approximately 500 g ofpolyethylene powder (ExxonMobil HDP8660) and approximately 500 g ofunbagged, dried cPBT pellets, which are shown in FIG. 1 (100).

The rotomolding oven was preheated to 315° C. and the mold rotated at 4rpm and 2.5 rpm on the major and minor axes, respectively. Theexperiment uses a ROTO-Lab Model 30 rotational molding machine,manufactured by MedKeff-Nye Company of Barberton, Ohio. The mold wasfitted with a temperature recording apparatus to measure the airtemperature of the interior of the mold. The mold was shuttled into theoven and rotated until the internal air temperature reached 250° C. Themold was then shuttled to a cooling chamber and immediately cooled witha combination of air and water to a temperature suitable for safe partremoval.

The procedure was repeated with the dried cPBT pellets sealed into twopolyethylene bags (Uline #S1520 4 mil poly bag), shown in FIG. 2 (200).FIG. 3 depicts the rotational mold (300) initially charged with PEpowder (302) and bagged cPBT (200).

The double-layer box made with unbagged cPBT in the initial charge had asignificant amount of embedded cPBT pellets in the outer PE layer. Incontrast, the double-layer box made with bagged cPBT in the initialcharge had virtually no embedded cPBT pellets in the outer PE layer.FIG. 4 shows the rotationally-molded box made with bagged and unbaggedcPBT. The box on the left (402) was made with unbagged cPBT, the outersurface of which clearly shows embedded cPBT particles (404). The box onthe right (406) was made with bagged cPBT, and the outer surface of thisbox is smooth and free of embedded cPBT particles (408).

Two-Layer Rotationally Molded Part: PE and Large Particle cPBT

A double-layer box with approximate dimensions 14″×10″×3.5″ wasrotomolded with a single charge containing PE and unbagged cPBTparticles. The same PE powder as used in the previous experiments wasused in this experiment. However, the cPBT particles used in thisexperiment were larger than the ¼″-long, ⅛″-diameter commerciallyavailable CBT160® pellets. The larger cPBT particles used in thisexperiment were irregular, dry pieces broken from an approximately 1″diameter strand collected from an extruder, (no water was adsorbed, sodrying was not required). The large cPBT particles were approximately ¾″to 1″ in length and approximately 1″ in diameter.

The rotomolding oven was preheated to 315° C. and the mold rotated at 4rpm and 2.5 rpm on the major and minor axes, respectively, using theROTO-Lab Model 30 rotational molding machine described above. The moldwas fitted with a temperature recording apparatus to measure the airtemperature of the interior of the mold. The mold was shuttled into theoven and rotated until the internal air temperature reached 250° C. Themold was then shuttled to a cooling chamber and immediately cooled witha combination of air and water to a temperature suitable for safe partremoval, for example, from about 30 to about 40° C.

The double-layer box made with unbagged ¼″-long, ⅛″-diametercommercially available CBT160® pellets in the initial charge had asignificant amount of embedded cPBT pellets in the outer PE layer, asshown in the left-hand box in FIG. 4, and described above. In contrast,the double-layer box made with large, unbagged ¾″ to 1″-long,1″-diameter cPBT pieces in the initial charge had virtually no embeddedcPBT pellets in the outer PE layer. The radius of the pieces were largerthan the thickness of the PE layer approximately ⅛″ thick, and the sizeand/or weight of the particles were sufficient to allow the particles to“pull out” of the melting/melted PE layer as the mold rotated for aperiod of time, allowing the PE layer to coat the inside of the moldsuch that the surface of the finished box did not reveal embedded cPBT.

EQUIVALENTS

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims. Insofar as this is aprovisional application, what is considered applicants' invention is notnecessarily limited to embodiments that fall within the scope of theclaims below.

1. A method of manufacturing a multi-layer part, the method comprisingthe steps of: (a) charging a rotational mold with at least thefollowing: a substantially non-oligomeric polymer for forming anexterior layer of the multi-layer part; and particles comprising amacrocyclic polyester oligomer for forming an interior layer of themulti-layer part, wherein the particles comprising the macrocyclicpolyester oligomer average at least about ⅛″ [3 mm] in at least onedimension; and (b) rotating the mold, the mold having an elevatedinterior temperature.
 2. The method of claim 1, wherein the particlescomprising the macrocyclic polyester oligomer average at least about ¼″[6 mm] in at least one dimension.
 3. The method of claim 1, wherein theparticles comprising the macrocyclic polyester oligomer average at leastabout ½″ [13 mm] in at least one dimension.
 4. The method of claim 1,wherein the particles comprising the macrocyclic polyester oligomeraverage at least about ¾″ [19 mm] in at least one dimension.
 5. Themethod of claim 1, wherein the particles comprising the macrocyclicpolyester oligomer average at least about ⅛″ [3 mm] in at least one ofthe following: thickness, length, and diameter.
 6. The method of claim1, wherein the particles comprising the macrocyclic polyester oligomerare contained within one or more plastic bags.
 7. The method of claim 6,wherein during step (b), the substantially non-oligomeric polymer beginsto melt before the macrocyclic polyester oligomer and before the plasticbag.
 8. The method of claim 1, wherein at least half of the particlescomprising the macrocyclic polyester oligomer are larger in at least onedimension than the thickness of the exterior layer of the multi-layerpart.
 9. The method of claim 1, wherein the particles are substantiallyspherical.
 10. The method of claim 1, wherein the particles aresubstantially cylindrical.
 11. The method of claim 1, wherein theparticles have an irregular shape.
 12. A method of manufacturing amulti-layer part, the method comprising the steps of: (a) charging arotational mold with at least the following: a substantiallynon-oligomeric polymer; and a macrocyclic polyester oligomer, whereinthe macrocyclic polyester oligomer is initially contained within one ormore plastic bags; and (b) rotating the mold, the mold having anelevated interior temperature.
 13. The method of claim 12, wherein thesubstantially non-oligomeric polymer comprises at least one of thefollowing: polyethylene, crosslinked polyethylene, polybutylene,polypropylene, polystyrene, polyethylene terephthalate, polybutyleneterephthalate, polyamide, polyester, polyvinyl chloride, polycarbonate,acrylonitrile butadiene styrene, nylon, polyurethane, polyacetal, andpolyvinylidene chloride.
 14. The method of claim 12, wherein themacrocyclic polyester oligomer comprises a macrocyclic poly(alkylenedicarboxylate) oligomer having a structural repeat unit of the formula:

where A is an alkylene, or a cycloalkylene or a mono- or polyoxyalkylenegroup; and B is a divalent aromatic or alicyclic group.
 15. The methodof claim 12, wherein the macrocyclic polyester oligomer comprises atleast one of the following: macrocyclic poly(butylene terephthalate)oligomer, macrocyclic poly(propylene terephthalate) oligomer,macrocyclic poly(cyclohexylenedimethylene terephthalate) oligomer,macrocyclic poly(ethylene terephthalate) oligomer, macrocyclicpoly(1,2-ethylene 2,6-naphthalenedicarboxylate) oligomer, andcopolyester oligomer comprising two or more monomer repeat units. 16.The method of claim 12, wherein the substantially non-oligomeric polymercomprises polyethylene and the macrocyclic polyester oligomer comprisesmacrocyclic poly(butylene terephthalate) oligomer.
 17. The method ofclaim 12, wherein the melting temperature of the macrocyclic polyesteroligomer is higher than the melting temperature of the non-oligomericpolymer.
 18. The method of claim 12, wherein step (a) further comprisescharging the mold with a filler.
 19. The method of claim 18, wherein thefiller comprises at least one of the following: a polymerizationcatalyst, a cross-linking agent, glass, glass fiber, milled glass fiber,glass microspheres, micro-balloons, stone, crushed stone, nanoclay,graphite, carbon nanotubes, carbon black, carbon fibers,buckminsterfullerene, anhydrous talc, fumed silica, titanium dioxide,calcium carbonate, wollastonite, chopped fiber, fly ash, linear polymer,monomer, branched polymer, engineering resin, impact modifier,organoclay, and pigment. 20.-30. (canceled)
 31. A method ofmanufacturing a part with a scratch-resistant surface, the methodcomprising the steps of: (a) contacting a surface of a rotational moldwith melted macrocyclic polyester oligomer; and (b) following step (a),introducing a substantially non-oligomeric polymer into the mold. 32.The method of claim 31, wherein step (a) comprises introducing solidparticles comprising the macrocyclic polyester oligomer into the moldand melting the solid particles in the mold.
 33. The method of claim 31,wherein step (a) comprises introducing melted macrocyclic polyesteroligomer into the mold.
 34. The method of claim 31, wherein step (b)comprises using a drop box to introduce the substantially non-oligomericpolymer into the mold. 35.-36. (canceled)
 37. The method of claim 31,wherein the substantially non-oligomeric polymer comprises at least oneof the following: polyethylene, crosslinked polyethylene, polybutylene,polypropylene, polystyrene, polyethylene terephthalate, polybutyleneterephthalate, polyamide, polyester, polyvinyl chloride, polycarbonate,acrylonitrile butadiene styrene, nylon, polyurethane, polyacetal, andpolyvinylidene chloride.